Ink comprising casein

ABSTRACT

A process for printing a porous substrate comprising ink jet printing a colorant and casein onto the substrate to give a print in which the colorant and casein are in contact with each other.

This invention relates to an ink jet printing process, to compositionssuitable for use in such a process, to printed substrate arising fromthe process and to the use of casein for improving the ozone fastness ofcolorants.

Ink jet printing is a non-contact process for forming an image on asubstrate by ejection of minute droplets of ink. Current substrates usedin ink jet printing are, in the main, papers coated with at least onereceptor layer to receive the ink. Such coated substrates tend to be oftwo fundamental types: non-porous media (also called swellable media)are those coated with swellable hydrophilic resins and porous media arethose coated with a high porosity surface. Porous media are becomingincreasingly popular in the ink jet industry as they offer keyadvantages over swellable media such as quicker dry times and hencefaster print speeds, improved water resistance and excellent control ofdot spread and hence resolution. A key and recently discovereddisadvantage of porous media has been poor ozone fastness for resultantimages compared to when swellable media are used. Hence, even in thedark, printed porous media tends to fade quicker than the swellablemedia equivalent.

We have found that the problem of poor ozone fastness for prints onporous media may be reduced or overcome by the process of the presentinvention.

According to the first aspect of the invention there is provided aprocess for printing a porous substrate comprising ink jet printing acolorant and casein onto the substrate to give a print in which thecolorant and casein are in contact with each other.

In one embodiment the colorant and casein are ink jet printed onto thesubstrate separately. In such embodiment it is preferred that thecolorant and casein are in printed from different ink jet cartridges orare printed from separate chambers of a one ink jet cartridge. This onecartridge prints the casein, for example as a composition comprising aliquid medium and casein but no colorant and a second ink jet cartridge,or a different chamber of the first ink jet cartridge, prints thecolorant, for example as a composition comprising a liquid medium andcolorant but no casein.

The order which the casein and colorant are applied can also have animpact on the ozone fastness of the resultant print. It is preferredthat the casein is printed first and the colorant is printed on top ofthe casein.

A more preferred embodiment is where both casein and the colorant areprinted onto the substrate simultaneously, for example an ink comprisingthe casein and colorant is printed onto the substrate. A preferred inkto achieve this comprises casein, colorant and a liquid medium.

An especially preferred embodiment is where casein is printed onto thesubstrate in a first step and a composition comprising casein andcolorant is printed onto the substrate in a second step to substantiallythe same area as the casein.

In all embodiments the casein is preferably applied as a compositioncomprising a liquid medium.

As colourants there may be mentioned pigments, dyes and mixturesthereof. Preferred colourants are dyes. Preferred dyes include azo,diazo, xanthene, anthraquinone, triaryl methane, azine, thiazine,phthalocyanine and nigrosine types. The dye preferably has a solubilityin the liquid medium of at least 10% by weight at 20° C. Preferably theamount of the colorant in the ink is 0.1 to 15%, more preferably 1 to10% and especially 2 to 8%, based on the total weight of the ink.

The liquid medium is preferably selected from water, organic solvent andmore preferably a mixture of water and organic solvent. The organicsolvent may comprise a mixture of different organic solvents. When theliquid medium comprises a mixture of water and organic solvent, theorganic solvent is preferably a water miscible solvent.

It is preferred that when the liquid medium comprises a mixture of waterand organic solvent that the weight ratio of water to organic solvent ispreferably from 99:1 to 1:99, more preferably from 99:1 to 50:50 andespecially from 95:5 to 70:30.

Preferred water-miscible organic solvents include C₁₋₆-alkanols,preferably methanol, ethanol, n-propanol, isopropanol, n-butanol,sec-butanol, tert-butanol, n-pentanol, cyclopentanol and cyclohexanol;linear amides, preferably dimethylformamide or dimethylacetamide;ketones and ketone-alcohols, preferably acetone, methyl ether ketone,cyclohexanone and diacetone alcohol; diols, preferably diols having from2 to 12 carbon atoms, for example pentane-1,5-diol, ethylene glycol,propylene glycol, butylenes glycol, pentylene glycol, hexylene glycoland thiodiglycol and oligo- and poly-alkleneglycols, preferablydiethylene glycol, triethylene glycol, polyethylene glycol andpolypropylene glycol; triosl, preferably glycerol and 1,2,6-hexanetriol;mono-C₁₋₄-alkyl ethers or diols, preferably mono-C₁₋₄-alkyl ethers ofdiols having 2 to 12 carbon atoms, especially 2-methoxyethanol,2-(2-methoxyethoxy)ethanol, 2-(2-ethoxyethoxy)-ethanol,2-[2-2-methoxyethoxy)ethoxy]ethanol,2-2[-(2-ethoxyethoxy)-ethoxy]-ethanol and ethyleneglycol monoallylether;cyclic amides, preferably 2-pyrrolidone, N-methyl-2-pyrrolidone;sulphoxides, preferably sulpholane. Preferably the liquid mediumcomprises water and 2 or more, especially from 2 to 8, water-solubleorganic solvents.

Especially preferred water-miscible organic solvents are cyclic amides,especially 2-pyrrolidone, N-methyl-pyrrolidone; diols, especially1,5-pentane diol, ethyleneglycol, thiodiglycol, diethyleneglycol andtriethyleneglycol; and mono-C₁₋₄-alkyl and C₁₋₄-alky; ethers of diols,more preferably mono-C₁₋₄-alkyl ethers of diols having 2 to 12 carbonatoms, especially 2-methoxy-2-ethoxy-2-ethoxyehtanol.

When the liquid medium comprises only organic solvent it is preferredthat it is free from water, (i.e. less than 1% water by weight).

When the liquid medium comprises only organic solvent it is preferredthat the solvent has a boiling point of from 30° to 200° C., morepreferably of from 40° to 150° C., and especially from 500 to 125° C.The organic solvent may be water-immiscible, water-miscible or a mixtureof such solvents. Preferred water-miscible organic solvents are any ofthe hereinbefore-described water-miscible organic solvents and mixturesthereof.

Preferred water-immiscible solvents include, for example: aliphatichydrocarbons; esters, preferably ethyl acetate; chlorinatedhydrocarbobs, preferably CH₂Cl₂; and ether, preferably diethyl ether;and mixtures thereof.

It is especially preferred that the liquid medium comprises water or amixture of water and one or more water-miscible organic solvent(s).

The porous substrate preferably has high levels of voids within itsstructure. These voids are useful for soaking up compositions containingcolorant.

The porous substrate can be purely organic but more preferably comprisean inorganic filler such as clay, calcium carbonate, magnesiumcarbonate, silica (especially surface modified silica), zeolite, aluminaor a combination of two or more thereof, and optionally a binder.

The weight ratio of the inorganic filler to binder in the poroussubstrate has a dramatic effect on the media porosity. Too much binderand porosity may be lost almost completely. Hence preferred weightratios of filler to binder in the porous substrate are preferably atleast 2:1 respectively, more preferably at least 3:1, especially atleast 4:1 and preferably up to 10:1.

Casein is a phospho-protein extracted from mammalian milk and accountsfor around 80% of the total protein content. The preferred casein isderived from cows' milk.

Various extraction methods exist but preferred caseins include acidcaseins, such as hydrochloric acid, sulphuric acid and lactic acidprecipitated caseins. Also useful is Rennet precipitated casein whereRennet is an enzyme. Other casein production methods such as Sheffieldand Spellacy continuous methods produce casein suitable for the presentinvention. The casein may also be a derivative thereof, e.g. a partiallyhydrolysed.

The casein may be in any salt form, e.g. the sodium, potassium, lithium,calcium or ammonium salt.

Casein is naturally colloidal and micellar. Casein derivatives may rangefrom micellar to fully soluble.

Preferred caseins are the fractions known as alpha (S1), alpha (S2),Beta and Kappa fractions.

Preferably the casein is printed onto the substrate in the form of acomposition comprising casein and a liquid medium.

Preferably the casein content in the composition is 0.1 to 10%, morepreferably 0.5 to 8% and especially 1 to 4% by weight based the totalweight of the composition and calculating the weight of casein on a 100%solids basis.

Since milk contains around 0.65% minerals, casein often contains metalion residues. Such residues are problematic, especially in thermal inkjet printing, and lead to kogation or long term firing problems.Divalent and trivalent ions are of particular concern.

Preferably the composition comprising casein and a liquid medium hasbeen purified to lower the content of divalent and trivalent metal ions.

More preferable is to use a casein which is substantially free from di-and trivalent metal ion.

Preferably the composition comprising casein and a liquid mediumcontains less than 0.1% di- and trivalent metal ions, more preferablyless than 0.05% and especially less than 0.01%, wherein all percentagesare by weight relative to the total weight of the composition.

Where an ink comprising casein and colorant is used in the process theink preferably comprises low levels of di- and trivalent metal ions.Thus, according to a second aspect of the present invention, there isprovided an ink comprising:

-   -   (i) 0.1 to 10 parts casein calculated on a 100% solids basis;    -   (ii) 0.1 to 15 parts colorant; and    -   (iii) 99.8 to 74.9 parts of a liquid medium;        wherein all parts are by weight, (i)+(ii)+(iii) add to 100 parts        and the ink comprises less than 0.1% by weight of di- and        tri-valent metal ions.

Since casein is highly susceptible to biological fouling anddegradation, the ink and composition preferably comprise a biocide.Preferred biocides are 1,2-benzisothiazolin-3-one (available as ProxelGXL™ from Avecia), Nuosept 95™ available from Hals America andglutaraldehyde available from Union Carbide.

Especially preferred is 1,2-benzisothiazolin-3-one.

Preferred levels of biocide are from 0.0001% to 0.1% and more preferably0.001% to 0.05% by weight relative to the total weight of the relevantcomposition.

Where an ink comprising casein and colorant is used in the process, amore preferred composition comprises 1,2-benzisothiazolin-3-one and lowlevels of di- and trivalent metal ions and. Thus according to a thirdaspect of the present invention there is provided an ink comprising:

-   -   (i) 0.1 to 10 parts casein calculated on a 100% solids basis;    -   (ii) 0.1 to 15 parts colorant;    -   (iii) 0.0001 parts to 0.1 parts of 1,2-benzisothiazolin-3-one;    -   (iv) a liquid medium;        wherein all parts are by weight, (i)+(ii)+(iii)+(iv) add up to        100 parts and the ink comprises less than 0.1% by weight of di-        and tri-valent metal ions.

The viscosity of the compositions and inks for use in the presentinvention are preferably less than 20 mPa.s, more preferably less than10 mPa.s and especially less than 5 mPa.s at 25° C.

Preferably compositions and inks for use in the present invention havebeen filtered through a filter having a pore size of less than 10 μm,more preferably less than 5 μm and especially less than 1 μm.

Preferably the surface tension of the compositions and inks for use inthe present invention are between 35 and 65 dynes per cm, morepreferably between 40 and 60 dynes per cm.

Compositions and inks for use in the present invention may optionallyfurther comprise a water-dissipatable binder. The binder may becolloidal or water-soluble.

The preferred binders in the inks, compositions and in the media includestarches, preferably hydroxy alkyl starches, for examplehydroxyethylstarch; celluloses, for example cellulose, methylcellulose,hydroxyethylcellulose, hydroxyproplycellulose, hydroxyethyl methylcellulose, carboxymethylcellulose (and salts thereof) and celluloseacetate butyrate; gelatin; gums, for example guar, xanthan hum and gumArabic; polyvinylalcohol; polyvinylphosphate, polyvinylpyrrolidone;polyethylene glycol; hydrolysed polyvinylacetate, polyethylene imine,polyacrylamides, for example polyacrylamide and poly(N,N-dimethylacrylamide) and polyacrylamido-2-methyl propane sulphonic acid);acrylamide-acrylic acid copolymers; polyvinylpyridine;polyvinylphosphate; vinylpyrrolidone-vinyl acetate copolymers; vinylpyrrolidone-styrene copolymers; polyvinyl;amine; poly(vinylpyrrolidonedialkylaminoalkyl alkylacrylates), for examplepolyvinylpyrrolidone-diethylaminomethylmethacrylate; acid-functionalacrylic polymers and copolymers, for example poly(meth)acrylic acid andcopolymers of (meth)acrylic acid and other (meth)acrylate monomers;amine-functional acrylic polymers and copolymers, for examplepolydimethylaminoethylmethacrylate; acid or amine functional urethanepolymers, for example those containing dimethylolpropanoic acid and/orpendant or terminal polyethylene glycols; ionic polymers, for examplepoly (N,N-dimethyl-3,5-dimethylene piperidinium chloride); polyesters,preferably those which carry water-solublising groups such as sulphonicacid groups, for example polyesters obtainable by polymerising a polyolwith sodiosulphoisophthalic acid.

Preferred water-dissipatable polymeric binders are: latex polymers, forexample cationic, non-ionic and anionic styrene-butadiene latexes; vinylacetate-acrylic co-polymer latexes; acrylic copolymer latexes whichcarry amino groups, for example containing co-polymeriseddimethylaminoethyl (meth)acrylate; and dispersions of polyester,polyurethane, (meth)acrylate or vinyl polymers and copolymers thereof.The polymer dispersions are preferably prepared by emulsionpolymerisation or by dispersion into water of polymers prepared bysuspension, bulk or solution polymerisation.

A combination of water-soluble polymeric binders and water-dissipatablepolymeric binders can be beneficial in terms of improved mechanicalstrength, reduced tendency for sheets to stick together and good inkabsorbency.

Overall particularly good results are found when the binder ispolyvinylalcohol, methylcellulose, polyvinylpyrrolidone, or anycombination thereof.

Composition(s) for the present invention may comprise general additivesknown in the art to improve ink-jet performance. Such additives includesurfactants, antifoamers, anticogation aids, biocides, dispersants,rheology modifiers, levelling agents, pH buffers and the like.

According to a fourth aspect of the present invention there is providedan ink jet printer cartridge comprising a chamber and a compositionaccording to the second or third aspect of the present invention.Preferred porous substrates suitable for use in the present inventioninclude Kodak Premium Ink Jet, Kodak Instant Dry PGP, Canon PR101, EpsonPremium GPP and Epson PGPP.

According to a fifth aspect of the present invention there is providedthe use of casein to improve the ozone fastness of a colorant,preferably a colorant existing as a print on a porous substrate. Thecasein may be used in any manner which brings the casein into contactwith a colorant for the purpose of enhancing ozone fastness, includingbut not limited to the process described in the first aspect of thepresent invention. The colorant may be any of those listed above,although preferably the colorant is a dye.

The invention of further illustrated by the following examples in whichall parts and percentages are by weight unless specified otherwise.

EXAMPLE 1 Ink 1—Preparation of an Ink Jet Ink Comprising Casein andPro-Jet™ Fast Cyan 2

Casein was dissolved in water by adjusting the pH to 10-12 using aqueoussodium hydroxide. To this solution was added Pro-Jet™ Fast Cyan 2,2-pyrolidone, thiodiglycol and Surfynol™ 465. The ink was adjusted to pH8-10 using NaOH to give an ink having the formulation: Component % byweight Pro-Jet ™ Fast Cyan 2 3 Casein 2 2-pyrolidene 5 thiodiglycol 5Surfynol ™ 465 2 water to 100The ink was loaded into an ink jet printer and applied to the substratesindicated in Tables 1 below.Comparative Ink

An ink was prepared in an identical manner to Example 1 except thatwater was used in place of casein.

The ink was applied to the substrates indicated in Tables 1 in anidentical manner to Example 1.

Tests

The following tests were performed on the prints obtained from Ink 1 andthe Comparative Ink:

Ozone Fastness

To evaluate ozone-fastness the prints were exposed to 100 parts perhundred million of ozone at 40° C. and 55% relative humidity for 24hours as sustained by a test cabinet supplied by Hampden Test EquipmentModel 903.

The optical density (OD) and CIE colour co-ordinates of each initialprint (a, b, L, Chroma “C” and hue “h”) were measured using a Xrite 983™ Spectrodensitometer with 0°/45° measuring geometry, with a spectralrange of 400-700 nm at 20 nm spectral intervals, using illuminant C,with a 2° (CIE 1931) observer angle and a density operation status of T.

After the ozone-fastness test, the OD and CIE colour co-ordinates wereremeasured. The degree of fade ΔE is defined as the overall change inCIE colour co-ordinates L, a, b of the print and is expressed by theequation: Δ  E = (Δ  L² + Δ  a² + Δ  b²)^(0.5)${The}\quad\%\quad{OD}\quad{loss}\quad{is}\quad{expressed}\quad{by}\quad\frac{\left( {{{OD}\quad{INITIAL}} - {{OD}\quad{AFTER}\quad{FADE}}} \right)}{{OD}\quad{INITIAL}} \times 100$

Lower values for ΔE and % OD loss represent less fade and better ozonefastness.

Ozone Fastness Results

The results are summarised in Table 1 below. TABLE 1 Casein SubstrateLevel ΔE % OD Loss Canon PR101 2% 11.50 28% Canon PR101 0% 52.10 85%Kodak PGP 2% 6.24 8% Kodak PGP 0% 34.30 62%

The prints obtained using casein showed much improved ozone fastness onporous media than the comparative ink which was free from casein.

1. A process for printing a porous substrate comprising ink jet printing a dye and casein onto the substrate to give a print in which the dye and casein are in contact with each other wherein the casein is applied as a composition comprising a liquid medium, the liquid medium comprises water and a water-miscible organic solvent, the weight ratio of water to water-miscible organic solvent is from 95:5 to 70:30 and the dye has a solubility in the liquid medium of at least 10% by weight at 20° C.
 2. A process according to claim 1 wherein the dye and the casein are printed onto the substrate separately.
 3. A process according to claim 1 wherein the dye and casein are in printed from different ink jet cartridges or are printed from separate chambers of a one ink jet cartridge.
 4. A process according to claim 1 wherein an ink comprising the casein and dye is printed onto the substrate.
 5. A process according to claim 1 wherein the casein is printed onto the substrate in a first step and a composition comprising casein and dye is printed onto the substrate in a second step to substantially the same area as the casein.
 6. A process according to claim 1 wherein the substrate has high levels of voids within its structure.
 7. A process according to claim 1 wherein the substrate comprises filler and binder in a weight ratio of at least 2:1.
 8. A process according to claim 7 wherein the filler is clay, calcium carbonate, magnesium carbonate, silica, zeolite, alumina or a combination of two or more thereof.
 9. A process according to claim 1 wherein the casein is substantially free from di and trivalent metal ions.
 10. An ink comprising: (i) 0.1 to 10 parts casein calculated on a 100% solids basis; (ii) 0.1 to 15 parts dye; and (iii) 99.8 to 74.9 parts of a liquid medium; wherein the liquid medium comprises water and a water-miscible organic solvent, the weight ratio of water to water-miscible organic solvent is from 95:5 to 70:30 and the dye has a solubility in the liquid medium of at least 10% by weight at 20° C., all parts are by weight, (i)+(ii)+(iii) add to 100 parts and the ink comprises less than 0.1% by weight of di- and tri-valent metal ions.
 11. An ink comprising: (i) 0.1 to 10 parts casein calculated on a 100% solids basis; (ii) 0.1 to 15 parts dye; (iii) 0.0001 parts to 0.1 parts of 1,2-benzisothiazolin-3-one; (iv) a liquid medium; wherein the liquid medium comprises water and a water-miscible organic solvent, the weight ratio of water to water-miscible organic solvent is from 95:5 to 70:30 and the dye has a solubility in the liquid medium of at least 10% by weight at 20° C., all parts are by weight, (i)+(ii)+(iii)+(iv) add up to 100 parts and the ink comprises less than 0.1% by weight of di- and tri-valent metal ions.
 12. A process according to claim 1 wherein the casein and dye are applied to the substrate in the form of an ink according to claim 10 or
 11. 13. An ink jet printer cartridge comprising a chamber and a composition according to claim 10 or
 11. 14. A method of improving the ozone fastness of a dye which comprises contacting the dye with casein. 